{"id":"F2006B10392","name":"AD/HS 125/114 - Generator Control Unit (GCU) Earth Wire","slug":"ad-hs-125-114-generator-control-unit-gcu-earth-wire","collection":"legislative_instrument","jurisdiction":"commonwealth","status":"in_force","isInForce":true,"actNumber":null,"makingDate":null,"administeringDepartment":null,"currentVersion":{"id":116049,"registerId":"commonwealth-F2006B10392-current","compilationNumber":null,"startDate":"2026-04-03","status":"InForce","reasons":null,"registeredAt":null},"sections":[{"sectionNumber":"1","sectionType":"section","heading":"AD/HS 125/114 - Generator Control Unit (GCU) Earth Wire","content":"---\nmeta-content-style-type: text/css\nmeta-content-type: application/xhtml+xml; charset=utf-8\nmeta-generator: Aspose.Words for .NET 22.10.0\n---\n\n?xml version=\"1.0\" encoding=\"utf-8\" standalone=\"no\"?>\n\nCOMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY\n\nSCHEDULE OF AIRWORTHINESS DIRECTIVES\n\n \n\n![](image.001.png)  British Aerospace BAe 125 Series Aeroplanes\n\n \n\nAD/HS 125/114 Generator Control Unit (GCU) Earth Wire 2/91\n\nDM\n\n \n\nApplicability: All BAe 125 aircraft as listed in the Requirement document. Requirement: Action in accordance with BAe SB 24-A278.\n\nNote: Compliance with this SB has been classified Mandatory by the UK CAA.\n\n \n\nCompliance: Prior to 31 January 1991.\n\n \n\nBackground: Loss of GCU earth connection can result in a DC generator overvoltage which can cause battery overheat and subsequent failure.\n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n\n \n","sortOrder":0}],"analysis":{"flash_summary":{"complexity_score":3,"scope_assessment":{"changed":false,"description":"The directive’s scope, as stated, matches the stated safety purpose: it applies to the BAe 125 aircraft listed in the referenced requirement document and mandates action per BAe SB 24-A278 to address the GCU earth-connection failure mode. The text provides no indication the scope has been expanded or narrowed from that stated intent."},"complexity_factors":["Dependence on an external technical document (BAe SB 24-A278) for the detailed work required","Applicability references a separate \"Requirement document\" for the exact list of affected airframes, creating a small gap to locate who is covered","Technical nature of work (electrical/GCU earth connection) requires specialised maintenance providers","Clear compliance deadline reduces procedural complexity but concentrates scheduling pressure"],"plain_english_summary":"What this directive does (mechanics)\n\n- Requires operators of affected British Aerospace BAe 125 series aeroplanes to carry out the work set out in BAe Service Bulletin (SB) 24-A278 (\"Requirement: Action in accordance with BAe SB 24-A278\").\n- Applies to all BAe 125 aircraft that are identified in the requirement document (\"Applicability: All BAe 125 aircraft as listed in the Requirement document\").\n- Sets a compliance deadline: the work must be completed before 31 January 1991 (\"Compliance: Prior to 31 January 1991\").\n\nOfficial reason given\n\n- The directive cites a safety risk: loss of the Generator Control Unit (GCU) earth connection can produce a DC generator overvoltage that may cause the battery to overheat and fail (\"Background: Loss of GCU earth connection can result in a DC generator overvoltage which can cause battery overheat and subsequent failure\").\n\nWho pays, who decides, and what behaviour changes\n\n- Who pays: aircraft owners/operators of the affected BAe 125s pay for the inspection/modification or other work required by BAe SB 24-A278 (the directive mandates the action but the SB specifies the technical work) (\"Requirement: Action in accordance with BAe SB 24-A278\").\n- Who decides: the Civil Aviation Safety Authority issues the airworthiness directive; compliance is achieved by following the manufacturer SB. Operators decide scheduling, contracting, and which maintenance provider performs the work, subject to the mandatory requirement and the compliance date (applicability and compliance provisions cited above).\n- Behaviour changes: operators must obtain and implement the SB instructions, schedule aircraft for the specified inspection/modification by the deadline, and document compliance.\n\nCosts, incentives and trade-offs (concrete mechanisms)\n\n- Direct costs: labour, parts, and possible aircraft downtime to perform the SB work. The directive does not specify cost or who supplies parts; those details are in the referenced SB (see \"Requirement: Action in accordance with BAe SB 24-A278\").\n- Incentives: compliance prevents the specified electrical fault; non-compliance risks regulatory action and continued exposure to the failure mode described in the background statement. The compliance deadline creates a time incentive to prioritise the work before 31 January 1991.\n- Opportunity cost: maintenance bays and personnel used for this work cannot be used for other tasks during that time; affected aircraft may be out of service while the work is done.\n- Implementation risk: the directive depends on the contents and availability of BAe SB 24-A278. The entry references a separate \"Requirement document\" for applicability; operators must consult that document to confirm whether a particular airframe is included (\"Applicability: All BAe 125 aircraft as listed in the Requirement document\").\n- Compliance burden and discretion: the directive is prescriptive as to the required action (follow the SB) and the deadline, leaving limited discretion to operators other than timing and choice of maintenance provider. Enforcement and verification rest with the regulator.\n\nEffects on private enterprise and competition\n\n- Maintenance market: independent maintenance organisations or the manufacturer can perform the SB work; the directive increases demand for qualified technicians and replacement parts for affected BAe 125s during the compliance window.\n- Prices and productivity: operators bear additional maintenance costs and potential short-term productivity loss from aircraft downtime. The directive does not set prices or exclusive providers.\n\nConcentrated benefits and diffuse costs\n\n- Benefits are concentrated on operators and their passengers (reduced risk of the specified electrical failure). Costs are concentrated on owners/operators of the affected BAe 125 aircraft rather than the wider aviation sector.\n\nNotes and practical points for operators\n\n- Operators must locate and follow BAe SB 24-A278 to know exactly what actions, parts, and record-keeping are required (\"Requirement: Action in accordance with BAe SB 24-A278\").\n- Operators must check the separate \"Requirement document\" to see whether a particular airframe is within the applicability list (\"Applicability: All BAe 125 aircraft as listed in the Requirement document\").\n- The directive was classified as mandatory by the UK Civil Aviation Authority in the note (\"Note: Compliance with this SB has been classified Mandatory by the UK CAA.\"), which supports the directive’s mandatory character but does not alter operational mechanics: the required action remains to follow BAe SB 24-A278 by the stated date."},"kimi_summary":{"content_quality":"ok","complexity_score":2,"scope_assessment":{"changed":false,"description":"This is a discrete, time-limited safety directive focused on a specific technical defect in a specific aircraft type. It has not expanded beyond its original purpose of mandating a wiring safety fix."},"complexity_factors":["Extremely short document (under 200 words)","Only 1 defined applicability (specific aircraft series)","Single, unambiguous compliance requirement (follow the Service Bulletin)","No cross-references to other legislation or regulations beyond the parent Civil Aviation Regulations 1998","No conditional logic, exceptions, or nested provisions","Clear, fixed compliance deadline","Plain language background explanation included"],"plain_english_summary":"**What this is:** This is an **Airworthiness Directive (AD)** — essentially a mandatory safety order issued by Australia's Civil Aviation Safety Authority (CASA) for specific aircraft.\n\n**What it does:** It requires owners and operators of **British Aerospace BAe 125 series aircraft** to carry out a specific safety fix on the **Generator Control Unit (GCU) earth wire** (the grounding/earthing wire that prevents electrical faults). The fix must follow instructions in a British Aerospace Service Bulletin (SB 24-A278).\n\n**Why it matters:** If the GCU earth wire fails or loses connection, the aircraft's DC generator can produce **overvoltage** — too much electrical power. This can cause the aircraft battery to overheat and fail, potentially leading to complete electrical system failure in flight.\n\n**Who must comply:** Anyone operating the affected BAe 125 aircraft had to complete this fix **before 31 January 1991**.\n\n**Key point:** This directive was classified as **mandatory** by the UK aviation regulator (CAA), and Australia adopted the same requirement to maintain safety standards."}},"importantCases":[],"_links":{"self":"/api/acts/ad-hs-125-114-generator-control-unit-gcu-earth-wire","history":"/api/acts/ad-hs-125-114-generator-control-unit-gcu-earth-wire/history","analysis":"/api/acts/ad-hs-125-114-generator-control-unit-gcu-earth-wire/analysis","conflicts":"/api/acts/ad-hs-125-114-generator-control-unit-gcu-earth-wire/conflicts","importantCases":"/api/acts/ad-hs-125-114-generator-control-unit-gcu-earth-wire/important-cases","documents":"/api/acts/ad-hs-125-114-generator-control-unit-gcu-earth-wire/documents"}}